This invention relates generally to apparatus or equipment for manufacturing glass containers, and, more particularly, pertains to an improved plunger assembly intended for use in what is known in the art as the press and blow process for glass bottle forming.
In the typical glass container manufacturing operation, gobs of molten glass are sequentially fed into a blank mould wherein each gob is subjected to an initial forming action. The gob is held in the blank mould and a plunger is inserted to form the gob into a parison by a pressing operation, after which the plunger is withdrawn and the parison is thereafter subjected to a blowing operation to complete the formation of the container.
It is currently typical in the art to utilize a plunger removably mounted on a piston-carried plunger head. The means of mounting the plunger to the plunger head usually comprises a pair of arcuate "split rings" which in their operative position abut to form a circular clamp surrounding the base end of the plunger and part of the plunger head. A surrounding cylinder in which the plunger assembly is reciprocally disposed, maintains the split rings in their operative position.
A prior art assembly as heretofore described is clearly illustrated in U.S. Pat. No. 4,033,744 issued to Robert Earl Davis on July 5, 1977, particularly in FIG. 1 of the drawings of that patent. The Davis patent is directed to the provision of a modified plunger assembly which eliminates the split rings and provides a rotable interlock between a plunger and a plunger head. The Davis assembly appears to offer definite advantages over the aforedescribed split ring concept but in use, it has proven to have certain inherent disadvantages which it was intended to correct. Because of the unreliable locking system between the plunger and the plunger head, users have found it necessary to originate additional cumbersome securing structure to maintain the plunger in operative position. Moreover, the Davis system will not accept adapted present components.
The prior art, in general, has many inherent shortcomings. There is no quick-change, self-aligning plunger mounting system available that is easily adapted to moulding equipment of different manufacturers. Because of wear characteristics inherent in the operation, expensive alloys are utilized for parts subjected to such wear. Present systems do not provide optimum alignment of the plunger relative to its support structure or the blank mould which results in non-uniform glass distribution.
Another problem associated with prior art equipment relates to the extreme inefficiency of air cooling of the plunger during its operation. The plunger is provided with an internal nozzle which receives a compressed air flow centrally upwardly therethrough. The air flow is distributed against the inside surface of the plunger and is exhausted downwardly through a series of relatively small exhaust ports provided through the mounting components. Air leakage at the point of merger between the various components is common. Such leakage and poor control of the air flow results in undesirable blow-by of exhausting air. A related problem is the need for excessive lubrication of the moving components to minimize wear. Build-up of lubricant and the random scattering of leaking air can be seen in excessive product specking.
In typical prior art equipment, optimum performance and positive positioning of the plunger are obtained when all components are new, but performance quality rapidly diminishes during use due to frictional scraping and scoring between contacting components.